1992 Chevrolet S-10 Blazer "Z"
Its winter time so i thought i would address this issue. My truck has no rear brakes, and the brake.light stays on. there must be a leak somewhere because about every month or so thberear of the master cylinder is empty. I havrnt been able to to find any leaks though. anybody know what this might be? the guy at oreillys said it might be some sort of pump but i never trust those guys.

 

Your combination valve has probably locked out your rear brakes due to a leak. There is an override on the end of it so you can bleed your brakes after its repaired.

 

Thank you for the infomation Now i just need to find the leak. I havent been able to find any leaks so far even after pumping the pedal.

 

usually if theres loss of fluid and youre 100% sure its not leaking out of any line, wheel cylinder of caliper its dumping into the brake booster out the back of the master cylinder. one easy way to check is pull off the vacuum line out of the booster and stick a long ziptie or piece of speaker wire in there, make sure its long enough to reach the bottom and pull it out and see if theres brake fluid on it. just go go poking around in there with a sharp screwdriver you can damage the booster. then again so can all that brake fluid in there

 

Thats an interesting theory. I will make sure i check that if ot warms up today or tomorrow. thanks!

 

i believe i have a rear brake issue as well. this i will check. where is the booster located? i've never noticed it. do they all look pretty universal? circular and all?

 

Somebody pleas correct if im wrong but im pretty sure the booster is the the big black rounded component thst the master cylinder is sticking out of on the fire wall

 

You got it.
HowStuffWorks "How Power Brakes Work"